Plummeting grades, weight change, trouble focusing, it might be easy to blame your teen's behavior on the changes in adolescence. Your family doctor might suspect attention deficit disorder. But Graves' disease, a condition where the thyroid works overtime, can easily be overlooked in kids and teens.

"I gained so much weight and I was so self-conscious about it," Alissa told ABC30.

Alissa's parents also noticed their daughter had a hard time staying on task.

"Even simple things, like my mom would tell me to go get her juice and she'd tell me a specific flavor and I'd walk to the fridge and I'd forget," Alissa told ABC30.

While Alissa's symptoms mimicked attention deficit disorder, the teen was actually struggling with a swing in thyroid hormones. At first her body didn't produce enough, and then it began to churn out too much.

Check a child's thyroid by having them look up at the ceiling. An enlarged thyroid will be obvious just above the collarbone.

Patients can take medication to help block the hormone production. Other options include radioactive iodine or surgery.

N. Scott Adzick, MD, Surgeon-in-Chief at the Children's Hospital in Philadelphia told ABC30, "There should be no recurrence risk of Graves' disease when you take the entire thyroid out."

Alissa had surgery to remove her thyroid gland. She says the "fog" she once had has lifted.

"My high school GPA was actually a 1.7, that's how bad I was doing in school," Alissa told ABC30.

Now she's an "A" and "B" student in college, making her father very proud.

Doctors say elevated heart rate and skin that is moist to the touch are also symptoms of Graves' disease. While most think of Graves' disease as an adult condition, one in 10,000 kids will be diagnosed or about 8,500 cases every year.